Various gene therapy approaches have been developed as alternatives to traditional protein therapy approaches. However, important challenges still remain in gene therapy. One of the major challenges of gene therapy is to achieve efficient influx of genes across plasma membranes (in animal cells) and nuclear membranes with minimal cytotoxicity.
Gene therapy systems can be broadly classified into viral vector-mediated systems and nonviral vector-mediated systems. Viral vectors are constructed using retroviruses or adenoviruses and have the advantage of high transfection efficiency into cells. However, viral vectors have problems associated with in vivo immunogenicity and suffer from inherent problems associated with genetic recombination. In attempts to overcome the stability problems of such viral vectors, various polymeric gene delivery systems have been developed as alternatives to traditional viral vector-based gene delivery strategies. For efficient gene delivery, polymeric vectors need to overcome intracellular trafficking barriers, such as endosomal escape and nuclear localization.
On the other hand, gene leakage occurs from synthetic peptide-based gene delivery systems in endosomal membranes at low pH, leading to DNA condensation and rapid endosomal escape. Accordingly, the use of synthetic peptide-based gene delivery systems can overcome the problems encountered with polymeric gene delivery systems. For such reasons, a variety of synthetic peptides have been developed to promote in vitro gene delivery in several cell lines. However, these synthetic peptides also suffer from the problems of toxicity and serum instability in in vivo applications.
As mentioned above, viral vectors have problems in immune response, self-replication, and in vivo stability and general polymeric vectors have the problems of high cytotoxicity and biotoxicity and low nucleic acid delivery efficiency due to their poor biocompatibility.
In this regard, research is being conducted on vectors using short cationic peptides. Even in this case, there are some problems, such as unstable DNA in extracellular spaces. Other problems of the vectors are poor stability of complexes with DNA and low gene expression level.
Under these circumstances, there is a need to develop a gene delivery vector specific for particular cells that possesses the ability to target particular cells and facilitates the influx of DNA into the target cells and the liberation of the DNA from a complex, achieving high expression level of the desired gene.
In this connection, adipocytes, particularly mature obese adipocytes, are final differentiated cells and are thus very difficult to transfect. In previous studies, electroporation has been used to transfect adipocytes but the transfection efficiency was reported to be only about 10%. Moreover, in in vivo gene delivery systems, this method has not been attempted to selectively deliver genes to target adipose tissues.
Thus, the present inventors have investigated non-viral gene delivery systems, and as a result, found for the first time a mechanism in which a peptide complex consisting of a particular peptide and an adipocyte-targeting sequence (ATS) binds to prohibitin expressed in mature adipocytes, directly targets obese adipocytes, delivers genes into the adipocytes, and promotes the expression of the genes, thus being suitable for the treatment of obesity and obesity-induced metabolic syndromes. The present invention has been accomplished based on this finding.